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Electronic circuits that use the 555 Timer

555 Timer Circuits

555 Timers are fun and a great way to start learning electronics

SCHMITT TRIGGER (Hysteresis) Circuit

Can also be called AN INVERTER or a SCHMITT INVERTER

We have animated the circuit to show how the output goes high or low according to the input level. The animation shows a wide gap between the input levels when the time when the output goes HIGH or LOW and this gap is called the HYSTERESIS GAP.
This circuit is called a SCHMITT TRIGGER and it is used in many building-blocks (using a different chip - such as 74c14) to prevent false triggering.
It prevents false triggering because as the input rises, the output does not change until the input voltage is fairly high. If the input voltage falls, the output does not change until the input falls about 30%. This means small fluctuations (noise) on the input do not have any effect on the output. The output is the INVERSE of the input - in other words the 555 is a SCHMITT INVERTER. The second diagram shows a Schmitt Trigger building block.


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